Double diffused metal oxide semiconductor device and manufacturing method thereof

ABSTRACT

The present invention discloses a double diffused metal oxide semiconductor (DMOS) device and a manufacturing method thereof. The DMOS device includes: an isolation structure for defining device regions; a gate with a ring-shaped structure; a drain located outside the ring; and a lightly doped drain, a source, and a body electrode located inside the ring. To increase the sub-threshold voltage at the corners of the gate, the corners are located completely on the isolation structure, or the lightly doped drain is apart from the corners by a predetermined distance.

CROSS REFERENCE

This is a Divisional of a co-pending application Ser. No. 13/066,622,filed on Apr. 20,2011.

The present invention claims priority to TW 100102809, filed on Jan. 26,2011.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a double diffused metal oxidesemiconductor (DMOS) device and a method of manufacturing the DMOSdevice; particularly, it relates to a DMOS device which has a gatehaving a ring-shaped structure, and a method of manufacturing the DMOSdevice.

2. Description of Related Art

FIGS. 1A-1C show a top view and two cross-section views of aconventional DMOS device, respectively. Referring to FIGS. 1A-1C, anisolation structure 12 (including multiple cross-sectional regions fromcross-section views) is formed in a P-type silicon substrate 11 todefine a first device region 100 and a second device region 200. Theisolation structure 12 for example is formed by local oxidation ofsilicon (LOCOS). A gate 13 having a ring-shaped structure is formed onthe substrate 11. A body region 14, a lightly doped drain 15, a bodyelectrode 16, and a source 17 are formed in the first device region 100,and a drain 18 is formed in the second device region 200. In normaloperation of the DMOS device, a channel is formed between the source 17and the drain 18. However, at the edges of the channel, in particulararound the corners of the ring-shaped structure of the gate 13, the bodyregion has a relatively lower concentration of the P-type impurities,and thus the impurities are diffused to a relatively smaller distance;in contrast, the lightly doped drain 15 which is doped with the N-typeimpurities has about similar concentrations at the corners of thering-shaped structure and in the middle of the channel. Therefore, whenthe DMOS device operates, the resistance around the corners of thering-shaped structure of the gate 13 is relatively lower, such that thecharacteristics of the DMOS device are adversely impacted as shown inFIGS. 2A and 2B. FIG. 2A shows the relationship between the gate voltageVg and the drain current Id in logarithmic scale. FIG. 2B shows therelationship between the gate voltage Vg and the drain conductance gm.From FIGS. 2A and 2B, it can be seen that due to the relatively lowerresistance around the corners of the ring-shaped structure, in realcondition, the DMOS device will turn ON at relatively lower gate voltageVg as indicated by the solid line, as compared to the ideal conditionindicated by the dash line. That is, the performance of the DMOS deviceis deteriorated in the real condition by the aforementioned cornereffect.

More specifically, FIG. 1C is a cross-section view taken along thecross-section line AA′ in FIG. 1A, which shows the middle of thechannel; and FIG. 1B is a cross-section view taken along thecross-section line BB′ in FIG. 1A, which shows the edge of the channel.As shown in FIG. 1B by the distance between the body region 14 and thegate 13, because the body region 14 has a relatively lower concentrationaround the corners of the ring-shaped structure, the impurities arediffused to a relatively smaller distance. In contrast, as shown in FIG.1C by the distance between the body region 14 and the gate 13, theimpurities concentration in the middle of the channel are relativelyhigher, and the body region 14 is diffused to a larger distance. Therelative locations of the body region 14 and the gate 13 in FIGS. 1B and1C indicate that the N-type impurities of the lightly doped drain 15 areless counter-doped by P-type impurities in FIG. 1B (at the edges of thechannel, in particular around the corners of the ring-shaped structure)than in FIG. 1C (middle of the channel). Hence, the resistance aroundthe corners of the ring-shaped structure is relatively lower and thesub-threshold voltage there is also relatively lower. In consequence,the DMOS device will turn ON at a relatively lower voltage as shown inFIGS. 2A and 2B, i.e., the threshold voltage of the DMOS device isreduced.

In view of the foregoing, the present invention provides a DMOS deviceand a method of manufacturing the DMOS device, to improve the drawbackthat the DMOS device turns ON at a lower threshold voltage, and toincrease the threshold voltage of the DMOS device; the present inventionimproves the parameters of the devices at the corners of the ring-shapedstructure, such that the DMOS device has a better performance.

SUMMARY OF THE INVENTION

The objectives of the present invention are to provide a DMOS device anda method of manufacturing the DMOS device.

To achieve the objectives mentioned above, from one perspective, thepresent invention provides a DMOS device, comprising: a substrate inwhich an isolation structure is formed for defining a first deviceregion and a second device region; a gate which is formed on thesubstrate and has a ring-shaped structure located along a boundary ofthe first device region, wherein the ring-shaped structure is completelyor partially inside the first device region from top view; a body regiondoped with first conductive type impurities, which is formed in thefirst device region in an area defined by the ring-shaped structure; alightly doped drain doped with second conductive type impurities, whichis formed in the body region; a source doped with the second conductivetype impurities, which is formed in the body region, interior of thelightly doped drain; a body electrode doped with the first conductivetype impurities, which is formed in the body region, interior of thesource; and a drain which is formed in the second device region; whereincorners of the ring-shaped structure are located completely on theisolation structure.

In a preferred embodiment, the ring-shaped structure is substantiallyrectangular and both the shorter sides of the ring-shaped structure arelocated completely on the isolation structure.

From another perspective, the present invention provides a DMOS device,comprising: a substrate in which an isolation structure is formed fordefining a first device region and a second device region; a gate whichis formed on the substrate and has a ring-shaped structure located alonga boundary of the first device region, wherein the ring-shaped structureis completely or partially inside the first device region from top view;a body region doped with first conductive type impurities, which isformed in the first device region in an area defined by the ring-shapedstructure; a lightly doped drain doped with second conductive typeimpurities, which is formed in the body region; a source doped with thesecond conductive type impurities, which is formed in the body region,interior of the lightly doped drain; a body electrode doped with thefirst conductive type impurities, which is formed in the body region,interior of the source; and a drain which is formed in the second deviceregion; wherein the lightly doped drain is apart from corners of thering-shaped structure by a predetermined distance.

In a preferred embodiment, the predetermined distance is not less thaneither a design rule critical dimension or 1 μm.

From another perspective, the present invention provides a method ofmanufacturing a DMOS device, comprising: providing a substrate in whichan isolation structure is formed for defining a first device region anda second device region; forming a gate on the substrate, the gate havinga ring-shaped structure located along a boundary of the first deviceregion, wherein the ring-shaped structure is completely or partiallyinside the first device region from top view; forming a body region inthe first device region in an area defined by the ring-shaped structure,the body region being doped with first conductive type impurities;forming a lightly doped drain in the body region, the lightly dopeddrain being doped with second conductive type impurities; forming asource in the body region, interior of the lightly doped drain, thesource being doped with the second conductive type impurities; forming abody electrode in the body region, interior of the source, the bodyelectrode being doped with the first conductive type impurities; andforming a drain in the second device region; wherein corners of thering-shaped structure are located completely on the isolation structure.

From another perspective, the present invention provides a method ofmanufacturing a DMOS device, comprising: providing a substrate in whichan isolation structure is formed for defining a first device region anda second device region; forming a gate on the substrate, the gate havinga ring-shaped structure located along a boundary of the first deviceregion, wherein the ring-shaped structure is completely or partiallyinside the first device region from top view; forming a body region inthe first device region in an area defined by the ring-shaped structure,the body region being doped with first conductive type impurities;forming a lightly doped drain in the body region, the lightly dopeddrain being doped with second conductive type impurities; forming asource in the body region, interior of the lightly doped drain, thesource being doped with the second conductive type impurities; forming abody electrode in the body region, interior of the source, the bodyelectrode being doped with the first conductive type impurities; andforming a drain in the second device region; wherein the lightly dopeddrain is apart from corners of the ring-shaped structure by apredetermined distance.

In a preferred embodiment, the DMOS device includes two lateral doublediffused metal oxide semiconductor (LDMOS) devices with a common source,or two double diffused drain metal oxide semiconductor (DDDMOS) deviceswith a common source.

The objectives, technical details, features, and effects of the presentinvention will be better understood with regard to the detaileddescription of the embodiments below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C show a top view and two cross-section views of aconventional DMOS device, respectively.

FIG. 2A shows a characteristic curve illustrating the relationshipbetween drain current and gate voltage of the conventional DMOS device.

FIG. 2B shows a characteristic curve illustrating the relationshipbetween drain conductance and gate voltage of the conventional DMOSdevice.

FIGS. 3A-3L show a first embodiment of the present invention.

FIGS. 4A and 4B show a second embodiment of the present invention.

FIGS. 5A-5H show a third embodiment of the present invention.

FIGS. 6A and 6B show a fourth embodiment of the present invention.

FIGS. 7A and 7B show a fifth embodiment of the present invention.

FIGS. 8A-8C show a sixth embodiment of the present invention.

FIGS. 9A-9C show a seventh embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The drawings as referred to throughout the description of the presentinvention are for illustration only, to show the process steps and theinterrelationship between the layers/parts, but not drawn according toactual scale.

Please refer to FIGS. 3A-3L, which show a first embodiment of thepresent invention. FIGS. 3A-3L are schematic diagrams showing themanufacturing process of a lateral double diffused metal oxidesemiconductor (LDMOS) device. FIG. 3B shows a cross-sectional view takenalong CC′ cross-section line shown in FIG. 3A. Referring to FIGS. 3A and3B, a first conductive type substrate 11 is provided. The substrate 11is for example but not limited to a P-type substrate. An isolationstructure 12 is formed in the substrate 12 for defining a first deviceregion 100 and a second device region 200. The isolation structure 12for example includes LOCOS regions as shown in FIG. 3B, or STI (shallowtrench isolation) regions.

Next, as shown in FIGS. 3C and 3D, a gate 13 is formed on the substrate11. The gate 13 has a ring-shaped structure from top view as shown inFIG. 3C. The ring-shaped structure is located along the boundary of thefirst area 100, and a part of the ring-shaped structure is locatedinside the first device region 100 from top view. Note that, both upperand lower sides of the ring-shaped structure of the gate 13 arecompletely located on the isolation structure 12 from top view shown inFIG. 3C. The aforementioned arrangement is for a reason that, referringto FIG. 3D which is a cross-sectional view taken along DD′ cross-sectionline shown in FIG. 3C, when the LDMOS device operates, because cornersof the ring-shaped structure are located on the isolation structure 12,the gate 13 will not partially turn ON, and there will be no significantleakage current at the corners of the gate 13.

In the next, referring to FIGS. 3E and 3F, a body region 14 is formed ina region defined by lithography and masked by the gate 13, byimplantation which implants first conductive type impurities, such asP-type impurities, in the form of accelerated ions to the definedregion.

Further next, referring to FIGS. 3G and 3H, a lightly doped drain 15 isformed in a region defined by lithography and masked by the gate 13, byimplantation which implants second conductive type impurities, such asN-type impurities, in the form of accelerated ions to the definedregion.

Next, referring to FIGS. 3I and 3J, spacers 13 a are formed on thesidewalls of the gate 13 by deposition and self-alignment etch. Furthernext, referring to FIGS. 3K and 3L, a body electrode 16 is formed in aregion defined by lithography and masked by the gate 13 and the spacers13 a, by implantation which implants first conductive type impurities,such as P-type impurities, in the form of accelerated ions to thedefined region. Referring to FIGS. 3K and 3L, a source 17 and drains 18are formed in regions defined by lithography and masked by the gate 13and the spacers 13 a, by implantation which implants second conductivetype impurities, such as N-type impurities, in the form of acceleratedions to the defined regions. Note that, the lightly doped drain 15, thesource 17, and the body electrode 16 are arranged from outside to insidewithin the ring-shaped structure from top view as shown in FIG. 3K, thatis, the source 17 is interior of the lightly doped drain 15 and the bodyelectrode 16 is further interior of the source 17, to form two LDMOSdevices which share the common source 17.

FIGS. 4A and 4B show a second embodiment of the present invention. Inthis embodiment, the upper and lower sides of the ring-shaped structureof the gate 13 are not completely located on the isolation structure 12in the LDMOS device; furthermore, as shown in FIG. 4A, the lightly dopeddrain 15 is apart from the upper and lower sides of the ring-shapedstructure by distances d and d′ respectively (d and d′ may be the sameor different). The aforementioned arrangement is for the same reason asthe first embodiment. Referring to FIG. 4B, which is a cross-sectionalview taken along EE′ cross-section line shown in FIG. 4A, when the LDMOSdevice operates, the gate 13 will not partially turn ON, and there willbe no significant leakage current at the corners of the gate 13. In apreferred embodiment, the distances d and d′ are not less than a designrule critical dimension, that is, the minimum width that can be definedby a lithography process in a manufacturing process for making the LDMOSdevice. A even preferred embodiment is that the distances d and d′ arenot less than 1 μm.

Referring to FIGS. 5A-5H, which show a third embodiment of the presentinvention. In this embodiment, the present invention is applied toanother type of DMOS device, i.e., a double diffused drain metal oxidesemiconductor (DDDMOS) device. FIGS. 5A-5H are schematic diagramsshowing the manufacturing process of the DDDMOS device. FIG. 5B shows across-sectional view taken along FF′ cross-section line shown in FIG.5A. Referring to FIGS. 5A and 5B, a first conductive type substrate 11is provided. The substrate 11 is for example but not limited to a P-typesubstrate. An isolation structure 12 is formed in the substrate 12 fordefining a first device region 100 and a second device region 200. Theisolation structure 12 for example includes STI regions as shown in FIG.5B, or LOCOS regions.

Next, as shown in FIGS. 5C and 5D, a gate 13 is formed on the substrate11. The gate 13 has a ring-shaped structure from top view as shown inFIG. 5C. The ring-shaped structure is located along the boundary of thefirst device region 100; however, all of the ring-shaped structure islocated inside the first device region 100 from top view. Further next,a body region 14 is formed in a region defined by lithography and maskedby the gate 13, by implantation which implants first conductive typeimpurities, such as P-type impurities, in the form of accelerated ionsto the defined region. Next, a lightly doped drain 15 is formed in aregion defined by lithography and masked by the gate 13, by implantationwhich implants second conductive type impurities, such as N-typeimpurities, in the form of accelerated ions to the defined region. Notethat, in this embodiment, the lightly doped drain 15 is apart from theupper and lower sides of the ring-shaped structure by at least a minimumdistance. FIG. 5D is a cross-sectional view taken along FF′cross-section line shown in FIG. 5C. Similar to the aforementionedembodiments, when the DDDMOS device operates, the gate 13 will notpartially turn ON, and there will be no significant leakage current atthe corners of the gate 13. In a preferred embodiment, the minimumdistance is not less than a design rule critical dimension, that is, theminimum width that can be defined by a lithography process in amanufacturing process for making the LDMOS device. A even preferredembodiment is that the minimum distance is not less than 1 μm.

Next, referring to FIGS. 5E and 5F, spacers 13 a are formed on thesidewalls of the gate 13 by deposition and self-alignment etch. Furthernext, referring to FIGS. 5G and 5H, a body electrode 16 is formed in aregion defined by lithography and masked by the gate 13 and the spacers13 a, by implantation which implants first conductive type impurities,such as P-type impurities, in the form of accelerated ions to thedefined region. Referring to FIGS. 5G and 5H, a source 17 and drains 18are formed in regions defined by lithography and masked by the gate 13and the spacers 13 a, by implantation which implants second conductivetype impurities, such as N-type impurities, in the form of acceleratedions to the defined regions. Note that, the lightly doped drain 15, thesource 17, and the body electrode 16 are arranged from outside to insidewithin the ring-shaped structure from top view as shown in FIG. 5G, thatis, the source 17 is interior of the lightly doped drain 15 and the bodyelectrode 16 is further interior of the source 17, to form two DDDMOSdevices which share the common source 17.

FIGS. 6A and 6B show a fourth embodiment of the present invention. Thisembodiment shows that the upper and lower sides of the ring-shapedstructure of the gate 13 in the LDMOS device are not only completely onthe isolation structure 12, but further apart from the edge of theisolation structure 12 with a larger distance than the first embodiment.That is, the corners of the ring-shaped structure do not have to connectto the body region 14, as seen from top view as shown in FIG. 6A andfrom cross-section view as shown in FIG. 6B, wherein FIG. 6B is across-sectional view taken along GG′ cross-section line shown in FIG.6A. The key point is that the edge of the channel is arranged so that,when the LDMOS device operates, the gate 13 will not partially turn ON,and there will be no significant leakage current at the corners of thegate 13. As long as the above purpose is achieved, the gate 13 can bedesigned in various shapes and is not limited to the rectangular shapeas shown in the aforementioned embodiments.

FIGS. 7A and 7B show a fifth embodiment of the present invention. Thisembodiment shows that the isolation structure 12 is formed by LOCOS.FIG. 7B is a cross-sectional view taken along HH′ cross-section lineshown in FIG. 7A. Similar to the aforementioned embodiments, when theDDDMOS device operates, the gate 13 will not partially turn ON, andthere will be no significant leakage current at the corners of the gate13.

FIGS. 8A-8C show a sixth embodiment of the present invention. Thisembodiment is different from the third embodiment in that, the DDDMOSdevice in this embodiment further includes drain extended regions (driftregions) 19. FIGS. 8B and 8C are cross-sectional views taken along II′and JJ′ cross-section lines shown in FIG. 8A, respectively. Thisembodiment shows that, the DDDMOS device may further include the drainextended regions 19 as part of the channel.

FIGS. 9A-9C show a seventh embodiment of the present invention. Thisembodiment is different from the sixth embodiment in that, the DMOSdevice in this embodiment does not include the drain extended region 19;instead, this embodiment includes a well 20, which is formed by blanketimplantation which implants second conductive type impurities, such asN-type impurities, in the form of accelerated ions to the substrate.FIGS. 9B and 9C are cross-sectional views taken along KK′ and LL′cross-section lines shown in FIG. 9A, respectively. This embodimentshows that, the DMOS device may further include the well 20 as part ofthe channel.

The present invention has been described in considerable detail withreference to certain preferred embodiments thereof. It should beunderstood that the description is for illustrative purpose, not forlimiting the scope of the present invention. Those skilled in this artcan readily conceive variations and modifications within the spirit ofthe present invention. For example, other process steps or structureswhich do not affect the primary characteristics of the device, such as adeep well, etc., can be added. For another example, the lithography stepdescribed in the above is not limited to photolithography by a photomask; it can be electron beam lithography, X-ray lithography, etc. Foranother example, the present invention may be also applied to two DMOSdevices with a common drain, as long as proper consideration is takensuch as the locations of the body region, the body electrode, and thelightly doped drain, etc. For another example, the present inventionalso may be applied to other devices which include a ring-shaped gate,not necessarily a DMOS device. In view of the foregoing, the spirit ofthe present invention should cover all such and other modifications andvariations, which should be interpreted to fall within the scope of thefollowing claims and their equivalents.

What is claimed is:
 1. A double diffused metal oxide semiconductor(DMOS) device, comprising: a substrate in which an isolation structureis formed for defining a first device region and a second device region;a gate which is formed on the substrate and has a ring-shaped structurelocated along a boundary of the first device region, wherein thering-shaped structure is completely or partially inside the first deviceregion from top view; a body region doped with first conductive typeimpurities, which is formed in the first device region in an areadefined by the ring-shaped structure; a lightly doped drain doped withsecond conductive type impurities, which is formed in the body region; asource doped with the second conductive type impurities, which is formedin the body region, interior of the lightly doped drain; a bodyelectrode doped with the first conductive type impurities, which isformed in the body region, interior of the source; and a drain which isformed in the second device region; wherein corners of the ring-shapedstructure are located completely on the isolation structure.
 2. The DMOSdevice of claim 1, wherein the ring-shaped structure is substantiallyrectangular and both the shorter sides of the ring-shaped structure arelocated completely on the isolation structure.
 3. The DMOS device ofclaim 1, wherein the DMOS device includes two lateral double diffusedmetal oxide semiconductor (LDMOS) devices with a common source, or twodouble diffused drain metal oxide semiconductor (DDDMOS) devices with acommon source.